The role of implicit theories in romantic relationships was investigated in two studies. People holding a soulmate theory, who believed that finding the right person is most important for a satisfying relationship, were compared to people holding a work–it–out theory, who believed that effort is most important for building a successful relationship. In Study 1, college students (N = 527) completed a set of questionnaires, including measures of relationship theories and functioning within romantic relationships. Approximately 8 months later, a subset of these students (N = 176) completed a second set of questionnaires for Study 1. The implicit theories were highly stable over time (r = .74). For soulmate theorists, feelings that one’s specific partner is ideal predicted relationship satisfaction and relationship longevity to a greater extent than for work–it–out theorists. Whereas Study 1 investigated people’s theories of relationships as ends of a bipolar continuum, a separate study explored people’s theories of relationships as two unipolar dimensions. Findings from Study 2 (N = 266) supported a representation of the theories as two negatively correlated factors, and supported findings from Study 1 highlighting the role of the interaction between the relationship theories and partner fit in predicting relationship satisfaction.